Cytosolic DNA induces type-I interferons and other cytokines that are important for immune defense against microbial infections and malignant cells but can also result in autoimmunity. This DNA signaling pathway requires the adaptor protein STING (Stimulator of Interferon Genes) and the transcription factor IRF3, but the mechanism of DNA sensing was unclear until recently. WO 2014099824 to The University of Texas disclosed that mammalian cytosolic extracts synthesized cyclic-GMP-AMP (cGAMP) in vitro from ATP and GTP in the presence of DNA but not RNA. DNA transfection or DNA virus infection of mammalian cells also triggered cGAMP production. cGAMP bound to STING, lead to the activation of IRF3 and induction of type-I interferons including interferon-β (IFN-β). Thus, cGAMP represents the first cyclic di-nucleotide in metazoa and it functions as an endogenous second messenger that triggers interferon production in response to cytosolic DNA.
Through biochemical fractionation and quantitative mass spectrometry, the inventors on WO 2014099824 also identified a cGAMP synthase (cGAS), which belongs to the nucleotidyltransferase family. Overexpression of cGAS activated the transcription factor IRF3 and induced IFN in a STING-dependent manner. Knockdown of cGAS inhibited IRF3 activation and IFN induction by DNA transfection or DNA virus infection. cGAS bound to DNA in the cytoplasm and catalyzed cGAMP synthesis. These results indicate that cGAS is a cytosolic DNA sensor that induces interferons by producing the second messenger cGAMP. The inventors on WO 2014099824 also determined that the second messenger cGAMP they isolated and synthesized contains two phosphodiester linkages, one between the 2′-OH of GMP and 5′-phosphate of AMP, and the othe between the 3′-OH of AMP and 5′-phosphate of GMP; this molecule is referred to as 2′3′-cGAMP.
Several additional patents applications in this field have henceforth published:
US20140205653 and US 20140341976 to Aduro Biotech disclose cyclic-di-nucleotide (CDN) compounds that activate and inhibit STING, respectively. In particular, the CDNs of the invention are provided in the form of a composition comprising one or more cyclic purine dinucleotides which activate or inhibit STING-dependent TBK1 activation and the resulting production of type I interferon.
WO 2015077354 A1 to The University of Chicago discloses Methods and compositions for treating cancer by intratumorally administering a stimulator of interferon genes (STING) agonist. In some embodiments, there are provided compositions and methods concerning methods for treating cancer in a subject comprising administering to the subject an effective amount of a stimulator of interferon genes (STING) agonist, wherein the STING agonist is administered intratumorally.
WO 2015161762 to Fudan University discloses the use of cyclic dinucleotide cGAMP for preparing antitumor drugs, wherein the tumor is gastric cancer, lung cancer, colon cancer, liver cancer, prostate cancer or pancreatic cancer. cGAMP was shown to inhibit the growth of human tumor cell lines in immune compromised mice.
WO 2015185565 to GlaxoSmithKline discloses a class of cyclic dinucleotide compounds, or a pharmaceutically acceptable salt and tautomers thereof, compositions, combinations and medicaments containing said compounds and processes for their preparation. The invention also relates to the use of said compounds, combinations, compositions and medicaments, in the treatment of diseases and conditions in which modulation of STING is beneficial, for example inflammation, allergic and autoimmune diseases, infectious diseases, cancer and as vaccine adjuvants.
WO 2014179335 to Memorial Sloan Kettering Cancer Center discloses compositions, methods, kits, and assays related to the use and/or exploitation of isomers of cGAMP as well as the structure of the enzyme cGAS.
There is still a need for the discovery and development of new cyclic di-nucleotide cGAMP analogs for use in medical therapy. Specifically, cGAMP analogues with better potency, stability and specificity than endogenous cGAMP are still needed. cGAMP analogues with superior safety and efficacy in animal models of human diseases, including cancer and infectious diseases, have yet to be developed.